1970's Infinity DSP Switching Amplifier ?? - diyAudio
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Old 22nd March 2006, 09:20 PM   #1
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Default 1970's Infinity DSP Switching Amplifier ??

Anyone know anything about this amp? Mine seems to have a power supply out. The unit wont come on at all. But I cant seem to find parts for it.
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Old 22nd March 2006, 09:22 PM   #2
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this is a picture of the amp in question http://cgi.ebay.com/1976-Infinity-DS...QQcmdZViewItem

I have the matching preamp. But I'm tackling one thing at a time.

First the Hafler, which I was able to fix with the help from you guys. Now this amp. But I just dont know much about it. it was given to me along witht the hafler amp and the matching Infinity preamp.
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Old 22nd March 2006, 10:00 PM   #3
lgreen is offline lgreen  United States
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Not sure if this is it or not-

Infinity Hybrid Amp (from PS Audio site).
Retired from DIY (2010) but still lurking now and again. My DIY audio projects- PartTimeProjects.com.
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Old 22nd March 2006, 10:05 PM   #4
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Igreen. Close but I have a picture of the amp in my previous post. thanks for the effort.
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Old 22nd March 2006, 10:20 PM   #5
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If I remember correctly, I think the designer (John Ulrick)of the Infinity Digital Amp now design the Spectron Amps. I could be wrong, but you can check with Spectron.
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Old 22nd March 2006, 10:26 PM   #6
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Thanks Quin, I will check.
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Old 4th May 2006, 05:17 AM   #7
hheier is offline hheier  United States
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Default Infinity SWA and Bel Canto Tripath Class T

Hello - Infinity SWA parts hard to find. John Ulrich at Spectron may be able to help.

What exactly is wrong with the power supply? It may be able to be repaired. I am currently seeking SWAs for spares. I found this forum and your post while searching for SWAs on the Internet. Please post if you decide to get out of it or if you have narrowed down what the problem is.

BTW - Recently heard the 1000 WATT Bel Canto monobloc using Tripath Class T digital switching technology. The Bel Canto has me rethinking Class D.
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Old 23rd January 2013, 10:59 PM   #8
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Cool Searching for an Infinity DSP Class D Amp

I am searching for the Amp. I have the Pre-Amp which I have faithfully had working for nearly 20 years. Looking for the matching Amp if anybody knows where I could find one, or if somebody would like to part with theirs.

-Earl Dryden
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Old 12th August 2015, 06:55 PM   #9
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To start troubleshooting one of these, you must find which module the fault is in. Remove the two channels and plug the power supply (still in the chassis) in. If it powers up, the trouble is in one of the channels. Unplug it and wait a few minutes and put one of the channels back in. If it powers up, plug the other channel in. Once this lets you know which module is bad, unplug the power supply and remove the module that is preventing power up. Check the output transistors with an ohm meter. If they are shorted they are SDT96305 transistors. The SDT96304 will work in a pinch but may not take the beating the SDT96305 can take. Be especially careful changing them as the ceramic insulator under them is FRAGILE! If you crack it, CAREFULLY piece it together and put the new transistor in and screw it down. check the two silver electrolytics on the board also. They can develop high ESR. The outputs are 80% of the time the problem and once repaired, will go for a couple of years and fail again. DO NOT PUT A MICA INSULATOR IN PLACE OF IT!!!!!!!
If the power supply won't power up, check the fuses on board. One is a 1/4 amp slow blow that can fail when the outputs fail or power supply troubles develop. The power supply has a diac and small amplifier that "kick starts" the larger supply. I have never seen that circuit fail. If the power supply just failed at low volume, there is a zener diode that fails near the large resistor towards the front of the power supply. It leaks and triggers the overvoltage protect which then blows the 1/4 amp fuse. If the power supply shut down when the amp was being driven hard and for a long time, one of the 40854 chopper transistors will short. I have used the SDT96304 to replace the bad one as well as a number of substitutes. It crosses to a vertical deflection transistor in early books. I can't find it in any of my RCA books. Also, the large bridge rectifiers can short. The power supply has one 20 amp fuse in the back and another inside. It will blow if the one on the back is replaced with too big of a fuse.
Most power supply failures I have encountered is caused by the amplifier being able to draw so much current momentarily that the AC line goes below 90 volts, forcing the switching duty cycle to 100% and shorting one of the 40854 transistors.
Bad solder is common with the age and it can cause hot spots on the power supply board.
The little lamps are just 6 volt grain of wheat lamps. They are a terror to change as they may melt themselves into the face. CAREFUL drilling of them will get them out. The mylar circuit board they mount on is FRAGILE. Use a good iron (Weller WTCP, 700 degree tip) to unsolder/install the new ones.
I bought my first SWAMP, serial # 00007 new. It is a red face. I have six SWAMPS, 4 operating and two I'm looking for parts for also. The hybrids will fail or go noisy if beaten from the input. I got the last two years ago from Infinity. They are a nightmare to replace. I knew John Uhlrick personally for many years and he was instrumental in helping me learn the SWAMP. All of the production SWAMPS are serially numbered on the channels, power supply and chassis. If you have one that is 1/4 inch shorter than the rest and has no serial numbers, from what I have learned, it was a late prototype. And no, they never finished the "display rate" circuit. The amp was discontinued before they could.
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